1. Field of the Invention
The invention relates to optical disk devices and, more particularly, to optical disk devices reproducing or recording information from multilayered optical disks having a plurality of signal recording layers.
2. Description of the Related Art
While a typical compact disk (CD) or a typical Compact Disk-Read Only Memory (CD-ROM) available at the present has a recording capacity of 640M bytes, a digital video disk (DVD) with a recording capacity of 4.7 Gbytes is also available with the recent increase in the density. A CD or CD-ROM has a thickness of 1.2 mm and a diameter of 12 cm. A DVD has half the thickness of a CD or CD-ROM, i.e. 0.6 mm, and has the same diameter that a CD or CD-ROM, i.e. 12 cm. There has also been proposed a dual layer DVD having its signal recording surface double-layered to obtain a recording capacity of 8.5 Gbytes (see e.g. Toshinori Kishi et al., xe2x80x9cDual-Layer Optical Disc Capable of Reading from a Single Sidexe2x80x9d, National Technical Report Vol. 41, No. 6, pp. 10-16, December 1995). The method of reproducing information from a dual layer optical disk having two recording layers or signal recording surfaces can include reproducing the information recorded on the two signal recording surfaces from one side of the disk and reproducing the information recorded on the two signal recording surfaces from their respective sides of the disk. The method of reproducing the information recorded on the two signal recording surfaces from their respective sides is, however, cumbersome, because the disk is required to be turned over in initially completing the reproduction of the information on one signal recording surface and then reproducing the information on the other signal recording surface. This method also fails to immediately reproduce the information on one signal recording surface when the information on the other signal recording surface is being reproduced. Thus, the technique of reproducing information recorded on two signal recording surfaces from one side of the disk is the mainstream of reproducing the information thereon.
As shown in FIG. 59, a one-side reading, dual layer optical disk has a reflective recording layer 1 formed of e.g. aluminum and having a reflectance of at least 70% and a translucent recording layer 2 formed, e.g., of gold and having a reflectance of approximately 30% and the two recording layers 1, 2 sandwich ultraviolet-ray hardened resin of approximately 40 xcexcm in thickness as an intermediate layer 3. On reflective recording layer 1 and translucent recording layer 2 is recorded such information as shown in FIG. 60. More specifically, the information includes data and ID. The ID includes address (track No.), layer information (layer number), and track information (track format information, area information, track system, reflectance).
Because the dual layer optical disk has one recording surface that is translucent, a laser beam can be radiated from one side of the disk and focused on each recording layer to read the information recorded on the recording layer via an optical pickup device.
Furthermore, for a dual layer optical disk, the so-called focus jump (see e.g. Japanese Patent Laying-Open No. 8-171731) is provided. More specifically, when the information on one recording layer is being reproduced an objective lens is moved in the direction of the optical axis so that the laser beam is refocused on the other recording layer to start reproduction of the information on the other recording surface.
The conventional focus jumping, however, has a disadvantage that access time is increased, because a targeted address is sought for after focus-jumping is performed.
Furthermore, the distance between the two layers of a dual layer optical disk is, in fact, not uniform over the entirety of the disk, varying in the radial direction. Thus, it is difficult to provide accurate focus-jumping at any location of the dual layer optical disk.
Furthermore, the conventional focus-jumping depends on the mechanical technique of employing an actuator for focusing servo control to move an objective lens in the direction of the optical axis. Thus, a long period of time is required to move the focal point of a laser beam from one recording layer to the other recording layer. There is also a problem that the conventional device often breaks down.
There is also a problem that if there is a pinhole or the like in a recording surface of a DVD, the layer information of an address is not clearly obtained and the layer of interest cannot be determined.
Furthermore, if the disk is damaged or suffers from surface aberration, a focusing error signal is not detected from its reflecting surface. Thus, the object lens will not be decelerated and disadvantageously collide with a surface of the disk.
One object of the present invention is to provide an optical disk device capable of accurate focus-jumping.
Another object of the present invention is to provide an optical disk device capable of reducing the time required for seeking a targeted address.
Still another object of the present invention is to provide an optical disk device capable of accurate focus-jumping at any location within a multilayer optical disk.
Still another object of the present invention is to provide an optical disk device capable of rapid focus-jumping.
Still another object of the present invention is to provide an optical disk device capable of identify each layer if a signal recording surface is damaged.
Still another object of the present invention is to provide an optical disk device capable of preventing an optical lens from colliding with a surface of an optical disk in focus-jumping.
According to the present invention, an optical disk device reproducing the information from an optical disk having the information recorded on a signal recording surface of a plurality of layers includes information reading means illuminating an optical disk with a beam via an objective lens and detecting a light reflected from the optical disk to read information, acceleration means producing and providing to the information reading means an acceleration signal for accelerating the objective lens in the direction of a normal to a signal recording surface of one of the plurality of layers to focus the beam on the signal recording surface of one layer when the information reading means is focusing the beam on a signal recording surface of another layer of the plurality of layers, and deceleration means producing and providing to the information reading means a deceleration signal for decelerating the objective lens when a focusing error signal obtained from the information reading means attains a predetermined level.
Preferably, the predetermined level is provided between the 0 level and peak level of the focusing error signal. The voltage of the deceleration signal is predetermined depending on the time taken from the generation of the acceleration signal by the acceleration means until the focusing error signal attains the predetermined level.
Preferably, the predetermined level is provided between the 0 level and peak level of the focusing error signal. Deceleration signal supply time is predetermined depending on the time taken from the generation of the acceleration signal by the acceleration means until the focusing error signal attains the predetermined level.
Preferably the deceleration means decreases the voltage of the deceleration signal stepwise.
Preferably the optical disk device also includes differentiation means differentiating the focusing error signal. The deceleration means varies the voltage of the deceleration signal depending on the maximal value of the focusing error signal differentiated.
Preferably, the optical disk device also includes storage means storing a plurality of predetermined levels of voltage of the deceleration signal corresponding to a plurality of maximal values of the focusing error signal differentiated, and reading means responsive to a maximal value of the differentiated focusing error signal for reading a corresponding level of the plurality of levels of voltage from the storage means. The deceleration means allows a voltage of the deceleration signal to be changed to the voltage read by the reading means.
In still another aspect of the present invention, an optical disk device reproducing information recorded on a signal recording surface of multiple layers of an optical disk includes information reading means illuminating the optical disk with a beam via an objective lens and detecting a light reflected therefrom to read information, acceleration means producing and providing to the information reading means an acceleration signal for accelerating the objective lens in the direction of a normal to a signal recording surface of one layer of the plurality of layers to focus the beam on the signal recording surface of one layer when the information reading means is focusing the beam on a signal recording surface of another layer of the plurality of layers, and deceleration means producing and providing to the information reading means a deceleration signal for decelerating the objective lens when a predetermined period of time has elapsed since the generation of the acceleration signal by the acceleration means.
In still another aspect of the present invention, an optical disk device reproducing the information recorded on a signal recording surface of multiple layers of an optical disk includes information reading means illuminating the optical disk with a beam and detecting a light reflected therefrom to read the information, drive means for moving the information reading means along the signal recording surface, acceleration means producing an acceleration signal for allowing the information reading means to focus on a signal recording surface of any of the plurality of layers when the information reading means is focusing on a signal recording surface of another of the plurality of layers, operation means in response to provision of a targeted address and the information on a targeted layer for calculating the shift in position of the information reading means from the current address and layer information from which the information reading means is reading information, and control means for driving the drive means to move the information reading means by the shift in position calculated and for allowing the acceleration means to produce the acceleration signal and providing the produced acceleration signal to the information reading means so that the information reading means focuses on a signal recording surface of the targeted layer.
In still another aspect of the present invention, a device reproducing the information recorded on a plurality of layers of an optical disk includes information reading means illuminating the optical disk with beam and detecting the light reflected therefrom to read the information, interlayer-distance detection means detecting a first spacing between layers of the mounted optical disk at a plurality of locations different in the distance from the center of the optical disk, storage means storing the first spacing detected by the interlayer-distance detection means, and control means controlling the information reading means to focus the beam on a second layer of the optical disk by calculating a second spacing between a first layer having its information being reproduced and the second layer depending on the first spacing stored in the storage means so that the information in the second layer is reproduced when the information in the first layer is being reproduced.
Preferably, the control means includes acceleration means producing and providing to the information reading means an acceleration signal for moving the information reading means to change the distance from the optical disk to the information reading means, and deceleration means producing and providing to the information reading means a deceleration signal having a variable magnitude for controlling the information reading means to stop at a position for focusing the beam on the second layer.
Preferably, the control means includes acceleration means producing and providing to the information reading means an acceleration signal having a variable magnitude for moving the information reading means to change the distance from the optical disk to the information reading means, and deceleration means producing and providing to the information reading means a deceleration signal for controlling the information reading means to stop at a position for focusing the beam on the second layer.
Still preferably, the control means includes acceleration means producing and providing to the information reading means an acceleration signal having a variable magnitude for moving the information reading means to change the distance from the optical disk to the information reading means, and deceleration means producing and providing to the information reading means a deceleration signal having a variable magnitude for controlling the information reading means to stop at a position for focusing the beam on the second layer.
Still preferably, the interlayer-distance detection means is provided to obtain a focusing error signal having two peaks different in polarity, and the control means produces and provides to the information reading means an acceleration signal for moving the information reading means to change the distance from the optical disk to the information reading means and also produces and provides to the information reading means a deceleration signal for controlling the information reading means to stop at a position for focusing the beam on the second layer to allow the acceleration signal provided to the information reading means to be switched to the deceleration signal at any point between the two peaks.
Preferably, the interlayer-distance detection means obtains a focusing error signal having two peaks different in polarity. The control means produces an acceleration signal for changing the distance from the optical disk to the information reading means and provides the acceleration signal to the information reading means until an intermediate point between the two peaks is reached, and the control means produces a deceleration signal for controlling the information reading means to stop at a position for focusing the beam on the second layer and provides the deceleration signal to the information reading means once the intermediate point between the two peaks has been reached.
In still another aspect of the present invention, a device reproducing the information recorded in a plurality of layers of an optical disk includes information reading means illuminating the optical disk with a beam and detecting the light reflected therefrom to read the information, acceleration means producing and providing to the information reading means an acceleration signal for moving the information reading means to change the distance from the optical disk to the information reading means, and deceleration means producing and providing to the information reading means a deceleration signal having a variable magnitude for controlling the information reading means to stop at a position for focusing the beam on a desired layer.
In still another aspect of the present invention, an optical disk device reproducing information from a multilayered optical disk having a plurality of recording layers includes a laser, an optical system including a lens directing a laser beam from the laser to the multilayered optical disk, and means changing the focal distance of the lens depending on the recording layer among the plurality of recording layers that has the information to be reproduced.
Preferably the lens is a collimator lens.
Preferably the collimator lens includes a first piece of lens, a second piece of lens provided opposite to the first piece of lens, and a transparent member interposed between the first and second pieces of lens. The means changing changes the refractive index of the transparent member depending on the recording layer among the plurality of recording layers that has the information to be reproduced.
Preferably, the transparent member includes a first transparent electrode, a second transparent electrode provided opposite to the first transparent electrode, and liquid crystal interposed between the first and second transparent electrodes. The means changing includes a liquid crystal drive circuit applying a predetermined voltage between the first and second transparent electrodes depending on the recording layer among the plurality of recording layers that has the information to be reproduced.
Preferably, the optical disk device also includes measuring means measuring a distance between the recording layers at a plurality of locations within the multilayer optical disk, storage means storing the distance measured with the measuring means together with the locations, and determination means determining the predetermined voltage according to the distance and locations stored in the storage means.
In still another aspect of the present invention, an optical disk device reproducing information recorded on the respective signal recording surfaces of first and second layers different at least in reflectance of an optical disk, includes information reading means illuminating the optical disk with a beam and detecting the light reflected therefrom to output any of a signal indicative of the read information, a focusing error signal and a tracking error signal, storage means previously storing a level of any of an output from the information reading means indicative of information read from the first and second layers, a focusing error signal and a tracking error signal, and discrimination means discriminating between the first and second layers by comparing any of the output from the information reading means indicative of the read information, a focusing error signal and a tracking error signal to the respective levels of the first and second layers when it is difficult to discriminate between the first and second layers.
In still another aspect of the present invention, an optical disk device reproducing information recorded on multiple signal recording surfaces of an optical disk includes information reading means illuminating the optical disk with a beam and detecting light reflected therefrom to read the information, acceleration means producing and providing to the information reading means an acceleration signal to allow the information reading means to focus on a signal recording surface of any layer of the plurality of layers when the information reading means is focusing on a signal recording surface of another of the plurality of layers, and deceleration means for producing and providing to the information reading means a deceleration signal for controlling the information reading means to stop in response to the fact that a predetermined reflected light cannot be obtained from the information reading means within a predetermined period of time after the acceleration means provides the acceleration signal to the information reading means.
In still another aspect of the present invention, an optical disk device reproducing the information recorded on a signal recording surface of a plurality of layers of an optical disk includes information reading means illuminating the optical disk with a beam and detecting a light reflected therefrom to read the information, acceleration means producing and providing to the information reading means an acceleration signal to allow the information reading means to focus on a signal recording surface of any of the plurality of layers when the information reading means is focusing on a signal recording surface of another of the plurality of layers, and the deceleration means for producing and providing to the information reading means a deceleration signal for controlling the information reading means to stop in response to the fact that a reflected light of a predetermined level cannot be obtained from the information reading means after the acceleration means provides the acceleration signal to the information reading means.
Preferably the deceleration means first controls the information reading means to stop and then the acceleration means again produces and provides the acceleration signal to the information reading means.
Preferably, the information reading means outputs an S-shaped curved signal as a signal indicating that focusing is achieved and the deceleration means produces the deceleration signal in response to the fact that the S-shaped curved signal cannot be obtained within a predetermined period of time.
Preferably the predetermined period of time is selected to a multiplication of the time required to allow focusing on a signal recording surface of any of the plurality of layers in response to the acceleration signal when another of the plurality of layers is being focused on.
Preferably, the reflected light of the predetermined level recited in claim 2 is selected to correspond to a fraction of the level of the reflected light obtained from the information reading means.